OxygenOS Open Beta 8 for the OP6 brings improvements to slow motion, a dedicated audio tuner for USB Type-C and Bluetooth earphones as well as other improvements in the UI. The OnePlus 6 does feature a 3.5 mm headphone jack unlike the new 6T but the new audio tuner is geared only towards USB Type-C and Bluetooth earphones. OnePlus claims that the new tuner will enable users to tweak audio specifically for their earphones/headphones without having to alter the audio profile across the system.

Open Beta 8 also includes the option of enabling systemwide dark mode in the Shelf dashboard. OnePlus did not dive into specifics of improvements in the slow-motion video but the overall quality of content shot at 480 fps 720p should look better.

And here is the full changelog for OxygenOS Open Beta 8 on the OnePlus 6, courtesy the OnePlus forum:

System

Audio tuner for Type-C and Bluetooth earphones

About Phone UI improvements

Communication

Improved UI for Call History

Launcher

Supported dark theme for Dashboard in Shelf

Camera

Improved slow motion

OnePlus also announced OxygenOS 9.0.7 for the OnePlus 6T simultaneously which brings a bunch of stability related improvements along with the audio tuner and the improvement to slow motion video.